Improvement in eye-pieces for telescopes



J'. W. NYSTROM.

EYE-PIECES FOR TELESCOPES.

Patented Nov. 16,1875.

Witnesses- UNITED STATES PATENT OFFICE.

JOHN W. NYS'IROM, OF PHILADELPHIA, PENNSYLVANIA.

IMPROVEMENT IN EYE-PIECES FOR TELESCOPES.

Specification forming part of Letters Patent No. 169,917, dated November 16, 1875; application filed October 19, 1875.

To all whom it may concern:

Be it known that I, JOI-IN W. NYsTROM, of the city and county ot' Philadelphia, in the State of Pennsylvania, have invented a new and Improved Eye-Piece for Telescopes, by which are secured permanent cross-hair lines, the eyeglass protected from dust or foul; and l hereby declare that the following is a full and exact description thereof, reference being had to the accompanying drawings and letters marked thereon.

The nature of my invention consists in placing the cross-hair lines in the field-lens ot' the eye-piece in such a manner that those lines are thoroughly protected from injury, and in .protecting the eyeglass from dust or fouly by a commodious cover, which is operated by slot motion.

In telescopes for field-instruments the crosshairs are generally made of spider-web, which is delicate to handle, and very often gets out ot' order, by which the instrument is rendered useless until new cross-hairs are replaced, which is adit'licult operation, and may delay the work in the tield, as the telescope must be readjusted for the new cross-hairs.

Cross-hair lines have been drawn on a llat piece ot' glass placed in the focus of the telescope, before the eye-piece, and, being also in the focus of the eyeglass, the slightest dust or t'oul settling on that ilat glass in the focus is seen through the eyeglass, and presents a disagreeable tield ot' observation.

In order to avoid the above-mentioned dil'li culties I make the field-lens of the eye-piece in two pieces, aiid draw the cross-hair lines on one oi` them, after which they are cemented together with said lines in the inside, and thus thoroughly protect them from injury. rlhe focus of the telescope is brought to the crosshair lines in the compound field-lens ot the eyepiece, and the focus oi' the eyeglass is also brought to the same lines, by which a clear iield is obtained. The dust or foul that may settle on the outer sides ot' the compound fieldlens is not seen through the eyeglass, because those sides are out ot' focus.

It is not customary, in engineering field-instruments, to protect the eyeglass from dust or foul, which may settle thereon and obscure the eld of observation. In spy-glasses the eyeglass is generally covered by a slide, which incoinmodiously projects outside of the eyepiece during the observation, or when the eyeglass is uncovered.

In order to avoid this difficulty I make a cover, which is moved over the eyeglass by a slot motion, so that said cover is not seen during the observation.

To enable others skilled in the art to make and use my invention, I will proceed to describe its construction and operation, reference being had to the accompanying drawings.

Figure 1 representsa side elevation ot the body E of the eye-piece screwed on the end ot' the telescope F. Fio. 2 represents a longitudinal section ot' the eye-piece, showing the eyeglass A, the compound held-lenses B X C, and the cover D.Y Fig. 3 represents an end view of the eye-piece, showing by the dotted lilies the cover D removed from the sight-hole G. Fig. 4 represents the end view ot' the eye-piece with the sight-hole piece L removed, showing the cover I) over the eyeglass A. Fig. 5 represents an end View ot' the eye-piece as seen from the telescope, showing the cross hair lines in the held-lens. Fin. 6 represents a perspective view ofthe compound field-lens, showing the position ofthe cross-hair lilies.

Like letters refer to like parts in all the figures.

'lhe field-lens is represented to be composed ot' two plano-convex lenses, B and O, Fig. 2, in which the cross-hair lilies X are drawn on either oneoi'the plane sides forming the joint; but it is not necessary that the two lenses should be plano convex, for either one ot' them may bc plane on both sides, or even concave, and the joint X may be made spherical, depending on the optical combination `of the teletope.

The lenses B and C may be placed loosely together in the cell; but, in order to thoroughly prevent dust or foul troni settling on the hair-lines, I prefer to cement the joint X with Canada balsam, or some other cement, making the compound lens perfectly transparent.

rIhe focus ot' the telescope is brought to X. where the tield is viewed through the eye'- glass A, which can be moved in or out by the sliding tube H to bring its focus to X. The

sliding,1 tube H has a slot for the screw I, to preventv it from being drawn out too fer. The eyeglass-cover D, Fig. 4, moves around the center or screw J fastened in the stationary part K. The part L L turns on e screw-joint between K and L. The screw M is fastened in the part L, and moves the cover D through the slot N, so that, by turning the part L, the cover D is moved to cover or uncover the eyeglass A, which should be uncovered onlywhen observations are made.

I claim as my inventionl. Alexis of the eye-piece provided with hairlnes, inclosed therein, substantially as set JOHN W. NYSTROM.

Witnesses: I

O. G. HEMPSTEAD, WM. O. HEMPsTEAn 

